How to improve dye fastness has become a research topic for engineering and technical personnel in the printing and dyeing industry. In particular, the light fastness of light-colored fabrics dyed with reactive dyes and the wet rubbing fastness of dark-colored fabrics; the decrease in wet processing fastness caused by post-dyeing thermal migration of disperse dyes; and high chlorine resistance, perspiration and light fastness There are many factors that affect color fastness, and there are many ways to improve color fastness. We have explored some methods and Measures have been taken to improve the dyeing fastness to a certain extent and basically meet the market demand.
Sunlight fastness of light-colored fabrics with reactive dyes
As we all know, reactive dyes dyed on cotton fibers will fade under sunlight. Under the attack of ultraviolet rays, the chromophores or auxochromophores in the dye structure will be damaged to varying degrees, resulting in discoloration or light color, which causes problems with light fastness.
National standards have already stipulated the light fastness of reactive dyes. For example, the GB/T411-93 standard for cotton printing and dyeing fabrics stipulates that the light fastness of dyed fabrics with reactive dyes is level 4-5, and the light fastness of printed fabrics is 4-5. The light fastness of GB/T5326 combed polyester-cotton blended printed and dyed fabrics and FZ/T14007-1998 cotton-polyester blended printed and dyed fabrics stipulates that the light fastness of disperse/reactive dyed fabrics is level 4, and the light fastness of printed fabrics is also level 4. It is difficult to reach this standard when dyeing light-colored fabrics with reactive dyes.
The relationship between dyeing matrix structure and light fastness
The light fastness of reactive dyes is mainly related to the parent structure of the dye. The parent structure of reactive dyes 70-75% of them are azo type, and the rest are quinone type, phthalocyanine type and A type.
Azo type has poor light fastness, while anthraquinone type, phthalocyanine type and azo type have better light fastness. The molecular structure of yellow reactive dyes is azo type, and the parent color bodies are pyrazolone and naphthalene trisulfonic acid, which have the best light fastness. The blue spectrum reactive dyes have anthraquinone, phthalocyanine, and toluene parent structures, and the sun fastness is the best. It has excellent light fastness and the molecular structure of the red spectrum reactive dye is azo type. Sunlight fastness is generally low, especially for light colors.
The relationship between dyeing concentration and light fastness
The light fastness of dyed samples will vary with the change of dyeing concentration. The same dye is used on the same fiber. The light fastness of dyed samples increases with the increase of dyeing concentration, which is mainly caused by the change in the size distribution of the aggregate particles of the dye on the fiber.
The larger the aggregate particles, the smaller the area of the dye per unit weight exposed to air and moisture, and the higher the light fastness.
The increase in dyeing concentration will increase the proportion of large particle aggregates on the fiber, and the light fastness will also increase accordingly. The dyeing concentration of light-colored fabrics is low, and the proportion of dye aggregates on the fiber is low. Most dyes are in a single-molecule state, which means the dye is highly decomposed on the fiber. Each molecule has the same chance of being exposed to light and air. , the effect of moisture, the light fastness also decreases accordingly.
ISO/105B02-1994 standard sunlight fastness is divided into 1-8 levels for evaluation. my country’s national standards are also divided into 1-8 levels for evaluation, AATCC16-1998 or AATCC20AFU standard Sunlight fastness is evaluated according to standards from 1 to 5. Therefore, we must first understand what standards the customer requires. The light fastness of dyed goods shown on the color cards provided by all dye manufacturers or companies, including the “Dye Index”, is measured at a dyeing depth of 1/1. The data is measured on medium-colored fabrics with a dye concentration of about 20-30g/L. Light-colored fabrics cannot reach this level.
Measures to improve the light fastness of light-colored fabrics
1. The selection of dyes has the most important influence on the light fastness of light-colored fabrics. The factor is the dye itself, so the choice of dye is the most important. When selecting dyes for color combinations, the light fastness of each component of the dye must be at the same level. As long as the light fastness of any one of the components, especially the component with the smallest amount, cannot reach the light fastness of light-colored dyes. If the requirements are met, the light fastness of the final dyed product will not meet the standard.
2. Other measures (1) The influence of floating dyes. Incomplete dyeing and soaping, unfixed dyes and hydrolyzed dyes remaining on the cloth will also affect the light fastness of the dyed goods. Their light fastness is significantly lower than that of fixed reactive dyes. The more complete the soaping is, the better the light fastness will be.
(2) The influence of color fixing agent and softening agent. When cationic low-molecular or polyamine-condensed resin-based fixatives and cationic softeners are used in fabric finishing, the light fastness of dyed goods will be reduced. Therefore, when selecting fixatives and softeners, attention must be paid to their impact on the light fastness of dyed materials.
(3) The influence of ultraviolet absorbers. Recently, UV absorbers are often used to improve the light fastness of light-colored dyed fabrics, but they must be used in large amounts to be effective. This not only increases the cost, but also causes yellowing and strong damage to the fabric, so it is best not to use this method.
Wet processing wet rubbing fastness of deep and concentrated colors of reactive dyes
Reactive dyes pass covalent Bonding gives dyes excellent color fastness, but dark and dense dyes often suffer from fading and staining. These phenomena occur in addition to the fact that part of the dye matrix structure is corroded by light, heat, sweat, acidic gases and oxidants. , decomposition of azo groups, detachment of complex metal ions, oxidation of amino groups, etc. may cause discoloration and fading of dyed goods. Breaking of dye-fiber bonds can also causeWhen the dosage greatly exceeds the saturation value, the excess dye cannot be dyed and fixed, and can only accumulate on the surface of the fabric, affecting the rubbing fastness of the fabric. Reactive dyes with high lifting power should be used to achieve a high dye uptake rate with a small amount. After testing the fabrics dyed by the above dyeing methods, it was found that the optimal color fastness is: dip dyeing > cold pad batch > wet short steaming > padding → drying → padding → steaming > padding → drying → steaming.
3. There are fixed dyes, floating dyes, residual alkali agents, electrolytes and other impurities inside and on the surface of the dyed fibers after washing treatment. Only when these impurities are removed can the dyed goods achieve optimal color fastness and color brightness. The method relies on water washing, soaping and mechanical external force. The purpose is to remove the hydrophilic floating color, wash away the electrolyte and alkali agent, reduce the electrolyte concentration to increase the electrostatic repulsion between the floating dye and the fiber, and make the floating dye more durable. It is easy to break away from the fiber; the alkali remover is to prevent the alkali agent from causing hydrolysis of the fixed dye during high-temperature soaping. Washing after soaping is to remove a large amount of floating dye that has been dispersed by the soaping agent. Water quality is very important in the post-treatment process. If the water hardness is high, there will be more heavy metal ions such as Ca2+ and Mg2+, which will change the color of the water-soluble sodium sulfonate salt into the insoluble calcium (magnesium) sulfonate salt. The water quality has a significant impact on the post-processing fastness of dyed materials.
4. Post-finishing is inherently deficient and will be compensated for later. The color fastness of the dyed fabric cannot meet the requirements and can only be compensated by using color fixing agents and enhancers in post-finishing. and improvement. The special fixing agent can improve the wet rubbing fastness of deep and concentrated reactive dyes by 0.5-1.0 levels.
Reactive dyes have poor chlorine fastness and sweat-light fastness
Reactive dyes generally have poor chlorine fastness. It mainly depends on the molecular structure of the color body. When there is a sulfonic acid group or carboxylic acid group in the ortho position of the diazo group of the dye, or when there is a sulfonic acid group or carboxylic acid group in the ortho or para position of the hydroxyl group of the coupling component, because of its The steric hindrance effect reduces the ability of CI- to attack -NH- or -N-, thus improving the chlorine resistance fastness.
According to the chlorine-resistant swimming pool water fastness test method of GB/T8433-1998, the available chlorine concentration is divided into three types: 20mg/L, 50mg/L and 100mg/L. Special requirements There are 200mg/L. As the available chlorine concentration increases, the chlorine fastness decreases. Therefore, dye selection is very important. Color fixing agents can also be used to improve the chlorine resistance fastness during the post-finishing process, but it can only increase by 0.5-1.0 levels. The perspiration-light fastness of reactive dyes has received great attention in recent years. Some reactive dyes have good light fastness, but poor perspiration and light fastness. Because under the dual effects of sweat and sunlight, the fading mechanism is different. Since the amino acids or related substances in the sweat chelate with the metal ions of the metal complex dye, they are separated from the dye matrix. The light fastness of the dye matrix before complexation is originally Not good, so it fades or changes color.
The decrease in fastness caused by thermal migration of disperse dyes after dyeing
Thermal migration phenomenon is the phenomenon of disperse dyes in two-phase solvents. A redistribution phenomenon, so all additives that can dissolve disperse dyes can produce thermal migration.
The reason for the thermal migration phenomenon is that the additives in the outer layer of the fiber dissolve the dye at high temperatures. The dye spreads from the inside of the fiber through the fiber capillary at high temperatures and migrates to the surface of the fiber, causing the dye to accumulate on the surface of the fiber. , causing a series of effects, such as discoloration, staining other fabrics when ironing, resistance to friction, washing, sweat stains, dry cleaning resistance and reduced color fastness to sunlight. Practice has shown that the amount of thermal migration of dyes from the inside of the fiber to the outside of the fiber is directly related to the dyeing depth. The deeper the dyeing depth of the fiber, the greater the amount of dye that thermally migrates from the inside to the outside, and the greater the impact on the dyed goods; high temperature treatment after dyeing has a greater impact on the dyeing. The thermal migration of disperse dyes has a greater impact, and the higher the temperature, the greater the impact.
Therefore, try to use gentle processes when finishing dyed fabrics. Thermal migration of disperse dyes is related to the molecular structure of the dye itself. Nonionic surfactants widely used in production practice are the main reasons for the thermal migration of disperse dyes.
Amino silicone emulsion is currently the most commonly used softener as a softener, because to make a microemulsion, it is necessary to apply 40-50% of the total silicone content of fatty alcohol polyoxyethylene ether or alkyl phenol. Nonionic surfactants such as polyoxyethylene ether are used as emulsifiers. With the widespread use of amino silicone emulsions, the post-dye thermal migration of disperse dyes is more serious. The solution is to choose disperse dyes with high lifting power and exhaustion rate, especially disperse dyes with good wet fastness after heat fixation of dyed goods.
Dye (floating color) attached to the fiber surface will aggravate the impact of thermal migration of dye on the color fastness of dyed fabrics. Therefore, after dyeing (especially dark colors), reducing agents and alkali agents should be used for reduction cleaning to completely remove floating colors.
Editor’s note:
In summary, in order to improve the color fastness of dyed goods, the selection of dyes is very important. Different dyes should be selected according to the requirements of color fastness. For dyes, light-colored fabrics with high requirements for light fastness should be dyed with vat dyes and reactive dyes with high light fastness; deep and dense colors can only be dyed with imported reactive dyes with high fixation rate and lifting power to ensure wet Processing fastness; for disperse dyes, dyes with low thermal migration should be selected. Especially for dark colors, try to avoid reaching or exceeding the dyeing saturation value. When using surfactants, we should adhere to the principle of “use less if you can, and use less if you can.” , when you have to use it, choose it carefully.”
Use less when you can, and when you must use it, choose carefully.”</p
